It is known to electrolyze tap water that has been provided with chloride ions, and thereby to generate acidic electrolyzed water at the positive electrode (anode). In general, acidic electrolyzed water contains available chlorine in equilibrium with a hypochlorous acid constituent. This acidic electrolyzed water has a strong sterilization effect on various types of microbes such as e-coli and other bacteria, and has recently begun to see increased use in medicine, agriculture, dairy industries, etc. The constituents that provide the sterilization effect in acidic electrolyzed water are chlorine gas, hypochlorous acid, and hypochlorite. Of these the sterilization strength of hypochlorous acid is highest. An additional advantage is that the acidic electrolyzed water can maintain the sterilization effect through long periods of storage.
Broadly speaking, the following two methods are described for electrolyzing water to produce acidic electrolyzed water that contains available chlorine and has strong sterilization capability:                (1) a method of generating acidic electrolyzed water that contains available active chlorine in the positive electrode chamber, by flowing tap water, into which a small amount of electrolyte containing chloride ions has been added, through both chambers of a two-chamber electrolysis apparatus which has a positive electrode chamber and a negative electrode chamber, separated by a permeable membrane to perform the electrolysis; and        (2) a method of generating acidic electrolyzed water by placing a liquid containing chloride ions in the center chamber of a three-chamber electrolysis apparatus, which is made up of a positive electrode chamber, a negative electrode chamber and a center chamber where, by passing tap water through both the positive electrode chamber and the negative electrode chamber, and applying a DC voltage to the positive electrode and negative electrode, the chloride ions in a chloride-containing electrolyte in the center chamber are caused to migrate to the positive electrode chamber, through the principle of electro-dialysis, generating acidic electrolyzed water that includes available active chlorine by the electrolysis reaction in the positive electrode chamber. Other methods are known, including an improved method described in JP 2005-175,654.        
The electrolytic reactions that occur on the surface of or near the positive electrode surface include both a desired reaction that generates chlorine gas from chloride ions, and the competing reaction of water that generates hydrogen ions and oxygen gas. Suppression of the reaction of water is important for increasing the production rate of chlorine gas needed to enhance the generation efficiency of available chlorine. Methods for performing this suppression of oxygen generation include                (1) placing the positive electrode plate and permeable membrane in close proximity to one another and generating effective electrolysis prior to the transmission of the chloride ion through the permeable membrane and its dispersal in a large amount of water; and        (2) restricting the amount of tap water for electrolysis passed through the positive electrode chamber with respect to the current applied, in order to increase the concentration of chloride ions in the positive electrode chamber and to increase the probability of the chlorine reacting. (These reactions are described in JP 3,113,645).        
In either of these methods the electrodes and the permeable membrane are placed as close together as possible to enhance the production efficiency of acidic electrolyzed water. However, with the permeable membrane and electrodes placed in close proximity in this manner, especially in the case where an ion exchange membrane is used as the permeable membrane, the ion exchange membrane and its supporting material deteriorate and break down more easily due to chlorination by chlorine gas generated at the electrode.